1. Field of the Invention
The present invention relates in general to insulation for exterior surfaces of aircraft, and in particular to airframe components for preventing thermal transfer through the exterior surfaces of aircrafts, such as hypercruisers and space launch vehicles.
2. Description of the Prior Arts
Prior art thermal protection systems include high temperature ceramic insulation blocks, or tiles, such as those used on the current reusable space shuttle orbiters Columbia, Challenger, Discovery and Atlantis to protect the shuttles during re-entry into the earth's atmosphere. These ceramic blocks are made from rigid fibrous high temperature ceramic materials which are brittle. Other prior art thermal protection systems have included standard insulation components covered by exterior metal panels. The exterior metal panels are joined together with sliding interfaces for accommodating thermal expansion of the exterior metal panels. The sliding interfaces between the metal panels are not sealed. Metal panels also tend to be relatively heavy, adding additional weight to the vehicle.
These types of prior art thermal protection systems are generally inadequate for use on the new hypersonic cruisers and space launch vehicles being currently developed, especially those which use cryogenic fuels. Liquid air and liquid oxygen will form on cryogenic fuel tank surfaces due to super cooling of atmospheric air. Also, new hypersonic cruisers and space launch vehicles will pass through the earths atmosphere at speeds in excess of Mach 6, and friction resulting from the aircraft travelling through the atmosphere will generate high temperatures on exterior surfaces of the aircraft.
A primary problem with prior art thermal protection systems is providing a moisture barrier over the range of temperatures encountered by these new aircraft. Currently, the ceramic blocks being used on the space shuttles have to be chemically retreated and reglazed after each flight in order to assure an adequate measure of waterproofing for a single flight. Deterioration of the moisture proofing for ceramic blocks will cause severe icing problems on cryogenic fuel tanks. There are also gaps or void spaces between the blocks to allow adequate room for thermal expansion of the high temperature ceramic materials from which the blocks are made. Moisture and other atmospheric constituents can travel inward along the spaces between the blocks.
Another problem is that the necessary thermal expansion spaces between ceramic blocks will create turbulence and excessive aerodynamic drag at airspeeds of Mach 6 and higher, causing a severe drag penalty for hypersonic cruise vehicles. Prior art metal panels having sliding interfaces have not been combined with prior art ceramic blocks because of incompatible coefficients of thermal expansion between the high temperature ceramic materials and the prior art metal panels. Since high temperature ceramic blocks are brittle, durability also will be a problem if the ceramic blocks are used for the outer surfaces of hypersonic cruise and space launch vehicles.